M. Langer and H. Woracek,
A characterization of intermediate Weyl coefficients,
Monatsh. Math. 135 (2002), 137–155

Abstract:
In connection with an indefinite analogue of canonical systems of differential equations some subclasses N0/Δ (Δ∈ℕ0) of the Nevanlinna class N0 come up. We give a criterion for a function to belong to N0/Δ in terms of its poles and residues.

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